The present invention relates to a silver halide photographic emulsion used in a silver halide photosensitive material and, more particularly, to a high-speed silver halide photographic emulsion superior in development dependence.
It is well known to use tabular silver halide grains (to be referred to as "tabular grains" hereinafter) or to use large-size silver halide grains in order to obtain a high-speed silver halide photosensitive material. However, raising the sensitivity by increasing the size of tabular grains is difficult because the equivalent-circle diameter of the grains extremely increases compared to common silver halide grains. One possible reason is that photoelectrons cannot be concentrated to one location because their diffusion length extremely increases, so no latent images can be efficiently formed. To solve this problem, U.S. Pat. Nos. 5,612,175, 5,612,176, 5,612,177, and 5,614,359 have disclosed a sensitization method which uses an epitaxial junction of silver chloride to large-size tabular grains. Unfortunately, this method using a silver chloride epitaxial junction has the problem that unstable solubility of the epitaxial portion increases the KBr dependence during development. So, the method cannot be widely used for general sensitized materials.
U.S. Pat. No. 5,709,988 has disclosed a sensitization method by which dislocation lines are introduced to fringe portions of tabular grains more densely than dislocation lines introduced to major surfaces of the grains. However, this method does not show any solution to delay of development caused by the increased size of tabular grains, although the sensitivity can be raised to some extent. That is, the magnitude of the processing dependence when large-size tabular grains are used is still unsolved.
U.S. Pat. No. 5,780,216 has disclosed a technique to improve the sensitivity/graininess ratio by a tabular grain emulsion having a multilayered structure of quintuple or higher-order. Unfortunately, in this patent the shell silver iodide content is as high as 15 to 40 mol %. Hence, development delay during processing cannot be solved even when the method is applied to large-size tabular grains used in the present invention.